Commercially available electrostatic copying machines or copiers, such as the copier shown in United States Published Patent Application No. B481,048, published Mar. 16, 1976 to J. A. Toto et al, now U.S. Pat. No. 3,988,542 generally include processing instrumentalities for forming and developing an electrostatic latent image on a moving photoreceptor and thereafter transferring the developed image from the photoreceptor to a copy sheet made of a suitable material such as paper.
For image developing purposes, many of such copiers are provided with magnetic brush developing apparatus of the type shown in U.S. Pat. No. 3,924,567, issued Dec. 9, 1975 to G. A. J. Koeleman et al, which generally includes a rotatable applicator for carrying developer to the latent image from a working supply of the same carried beneath the applicator in a suitable sump. The developer comprises a suitable toner material in powder form, and a suitable ferromagnetic material in granular or bead form to which the toner material is tribo-electrically attracted. In the course of each operating cycle of the copier, the rotating applicator lifts a portion of the working supply of developer from the sump and into contact with the latent image on the moving photoreceptor, as a result of which sufficient toner is transferred from the carrier to the latent image for developing the same.
To prevent the working supply of developer from becoming gradually useless due to dissipation of its toner and/or carrier content, the working supply is rejuvenated from time-to-time by adding a replenishing supply of developer. To that end, the copier is provided with developer dispensing means for replenishing the working supply of developer. As shown in U.S. Pat. No. 3,853,246 issued Dec. 10, 1974 to R. C. DuBois, a typical arrangement of such dispensing means comprises a bottle of developer adapted to be rotated from a source of supply of motive power. The rotating bottle dispenses developer into the sump of the magnetic brush apparatus for replenishment of the working supply.
To control the dispensing means there has been provided, as discussed in the aforesaid U.S. Pat. No. 3,924,567, a device which is responsive to the reflectivity of developer on the applicator, and associated circuitry for energizing the dispensing means when the reflectivity exceeds a predetermined level. In the prior art, a conventional comparator to which the reflectivity responsive device is connected has been utilized to directly operate a relay having a contact connected to gate a triac when controls the motor driving circuit of the dispensing means; thereby controlling rotation of the bottle of replenishing developer.
One of the problems which arises in the prior art is that since the applicator is depleted of developer until it commences rotation, and the reflectivity responsive device is operative for signaling the dispensing means before the applicator carries a sample of the developer past the reflectivity responsive device, the device signals the dispensing means to add developer to the magnetic brush sump whether or not the sump has a sufficient quantity of developer therein. Another problem of the prior art relates to the sensitivity of the circuitry associated with the reflectivity responsive device. As often as not the relay which is controlled by the low developer density signal from the comparator associated with the reflectivity responsive device, is energized and deenergized at such a rapid rate that the relay contact in the triac controlled motor drive circuit chatters, resulting in the motor noisily jogging the developer resupply bottle of the dispensing means. Accordingly:
An object of the present invention is to provide an improved developer supply control system for a copier;
Another object is to provide means for controlling the developer dispensing means in a copier of the type which includes magnetic brush developing means; and
Yet another object is to provide a copier including means for solving the above described problems in the prior art.